In HPLC, high-pressure switching valves are used for an entire series of different tasks, for example in order to remove a sample to be examined from a sample container, to feed it into a sample loop and, from there, to introduce it into a high-pressure liquid flow in the direction of a chromatography column, or in order to flush various components or in order to switch over between a plurality of columns.
Switching valves of this type are installed as a rule in automatic samplers for HPLC, in column ovens or in fraction collectors.
When switching valves are used, it is almost always advantageous if only short capillary paths, that is to say short lengths of capillaries which guide the medium to be switched, are required between the relevant components. For example, when samples are guided in an eluent flow, it is advantageous if only short capillary paths have to be overcome, since the dispersion of the sample, that is to say the mixing of the sample with the eluent which is situated upstream and downstream of the sample in the flow path, is then low. In addition, the pressure loss in the relevant system is minimized by short capillary paths.
In order to make short capillary paths possible, it is advantageous or indispensable in many cases if the switching valve is constructed so as to be as compact as possible. As a result, the switching valve can be used in a space-saving and variable manner.
Despite a compact construction, it goes without saying that a switching valve of this type also has to ensure precise and reproducible positioning of the moving parts which guide the medium to be switched.
Switching valves, as used for introducing a sample into the fluid stream, normally have a stator in which there are provided multiple connection ports for the supply and discharge of the fluid to and from the switching valve. The ports are connected via ducts to opening cross sections which are formed on a switching surface of the stator, for example in the face side of a substantially cylindrical stator element. The rotor likewise has a switching surface which interacts with the switching surface of the stator, wherein in the switching surface of the rotor there are formed grooves which serve to connect certain opening cross sections and/or ports of the stator to one another as a function of two or more switching positions. Here, the rotor and the stator must be pressed against one another with an adequately high pressing force in order to attain a sealing action in the plane of the switching surfaces even in the case of high pressures such as arise in liquid chromatography, in particular HPLC.
Such switching valves are described for example in WO 2009/101695 A1 or US 2010/0281959 A1.